Improve Index Body Template Events

This is an update to http://tracker.phpbb.com/browse/PHPBB3-12014

Adding another event to give it before and after event locations, but this also means renaming the events.

In prosilver/subsilver2 styles, these events are not bookending breadcrumbs, but the link lists that appear at the top of the index page, before the forum list (the search unanswered, search your posts links, MCP, ACP links, etc.) so I'm renaming them:

index_body_linklist_before/after.